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#ifndef QPID_FRAMING_VISITOR_H
#define QPID_FRAMING_VISITOR_H
/*
* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements. See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership. The ASF licenses this file
* to you under the Apache License, Version 2.0 (the
* "License"); you may not use this file except in compliance
* with the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing,
* software distributed under the License is distributed on an
* "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
* KIND, either express or implied. See the License for the
* specific language governing permissions and limitations
* under the License.
*
*/
#include <boost/mpl/vector.hpp>
#include <boost/type_traits/remove_reference.hpp>
#include <boost/preprocessor/seq/for_each.hpp>
namespace qpid {
namespace framing {
/** @file Generic visitor pattern. */
/** visit() interface for type T (optional return type R, default is void.)
* To create a visitor for a set of types T1, T2 ... do this:
* struct MyVisitor : public Visit<T1>, public Visit<T2> ... {};
*@param T Type to visit. This must be forward declared, and need not be defined.
*/
template <class T, class R=void> struct Visit {
typedef R ReturnType;
typedef T VisitType;
virtual ~Visit() {}
virtual R visit(T&) = 0;
};
#define QPID_VISITOR_DECL(_1,_2,T) class T;
#define QPID_VISITOR_BASE(_1,_2,T) , public ::qpid::framing::Visit<T>
/** Convenience macro to generate a visitor interface.
* QPID_VISITOR(MyVisitor,(A)(B)(C)); is equivalent to:
* @code
* class A; class B; class C;
* class MyVisitor : public Visit<A> , public Visit<B> , public Visit<C> {};
* @endcode
* @param visitor name of the generated visitor class.
* @param bases a sequence of visitable types in the form (T1)(T2)...
* Any parenthesized notations are due to quirks of the preprocesser.
*/
#define QPID_VISITOR(visitor,types) \
BOOST_PP_SEQ_FOR_EACH(QPID_VISITOR_DECL, _, types) \
class visitor : public ::qpid::framing::Visit<BOOST_PP_SEQ_HEAD(types)> \
BOOST_PP_SEQ_FOR_EACH(QPID_VISITOR_BASE, _, BOOST_PP_SEQ_TAIL(types)) \
{}
/** The root class for the hierarchy of objects visitable by Visitor V.
* Defines virtual accept().
*/
template <class V, class R=void>
struct VisitableRoot {
typedef V VisitorType;
typedef R ReturnType;
virtual ~VisitableRoot() {}
virtual R accept(V& v) = 0;
};
/** The base class for concrete visitable classes.
* Implements accept().
* @param T type of visitable class (CRTP).
* @param Base base class to inherit from.
*/
template <class T, class Base>
struct Visitable : public Base {
void accept(typename Base::VisitorType& v) {
static_cast<Visit<T>& >(v).visit(static_cast<T&>(*this));
}
};
}} // namespace qpid::framing
#endif /*!QPID_FRAMING_VISITOR_H*/
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